The present invention relates to a polyester bottle having a handle mounting portion of the bottle body being fixed by heat (heat treatment) which has advantageous heat resistance, and the method of manufacturing such bottle.
Plastic bottles have widely been used as bottles for a variety of liquids as they are light in weight and have high shock resistance characters. Particularly, bottles molded by biaxially blow stretching a thermoplastic polyester such as a polyethylene terephthalate not only has good transparency and surface gloss, but are also equipped with the shock resistance, the strength, the gas barrier characters all needed in a bottle, so it is widely used as bottles for liquids such as juice, soft drinks, carbonated beverages and the like.
However, the polyester bottle has a problem in that it has low heat resistance, and when heat-filling the contents, the bottles were likely to be deformed at times by heat, or the capacity may be changed by shrinking. Therefore, there was a need to mold the bottle body by a biaxial stretch blow, and then to perform a heat fix (heat treatment) in order to increase the heat resistance. As a method for such heat treatment, many suggestions were made in the prior art, and a known method, for example, increases the heat resistance by providing heat treatment to the bottle in a mold for blow molding heated to a high temperature.
The heat treatment inside the mold heated to a high temperature is industrially advantageous since there are only a small number of steps to be carried out, and the cost of the device is low. However, for the heat treatment after the blow molding and the following cooling step, it is necessary to take a long residence time inside the mold, which leads to a longer molding cycle, and results in low manufacturing speed.
Further, the higher the mold is heated, the improved the effect of the heat treatment becomes, but when the mold is heated to a high temperature, an oligomer is precipitated from the bottle and adheres to the mold, which not only ruins the appearance of the produced bottle but also reduces productivity since there is a need to wipe away the oligomer on the surface of the mold regularly. This lowers the manufacturing speed even further.
On the other hand, a polyester bottle having a handle body fixed on the bottle body is used for an easier handling of the bottle. One method to mount the handle body to the bottle body is to set a preform for molding the bottle body to a cavity of a mold for molding the bottle with a handle body being set thereto which has been molded in advance by an injection molding and the like, and by blowing air into said preform for blow molding, forming the bottle body and connecting the handle body to the handle mounting portion of the bottle body. The second method performs blow molding to said preform set to said cavity of the mold, forming a bottle body having a handle mounting portion, and then by forming a handle body by injection molding, matching and fixing the handle body to said handle mounting portion.
However, by applying a method of providing heat treatment by heating the mold in the above mentioned method, the wall surface of the handle mounting portion of the bottle body will not contact the highly heated mold because of the handle body mounted thereto, so the wall surface of the handle mounting portion will not be heat treated, and the handle mounting portion will not be provided with a sufficient heat resistance. Therefore, at the time of heat-filling, there was a problem that the handle mounting portion will shrink or deform, and the mounting strength of the handle will be reduced.